This section provides background information related to the present disclosure which is not necessarily prior art.
Vehicle manufacturers often install multi-layer noise insulation mats in automobiles to quiet the passenger compartment of the vehicle. Such multi-layer noise insulation mats, also referred to as noise attenuation systems, are typically made of foam and/or “shoddy” material built up for lightweight constructions. Thicknesses of these multi-layer noise insulation mats typically range from 0.25 inches to multiple inches.
One such noise insulation mat is disclosed by Gahlau et al. in U.S. Pat. No. 4,655,496 entitled “Motor Vehicle Noise Insulation.” As shown in this reference, such noise insulation mats are often applied in a blanket form to cover surface areas of the vehicle such as the engine firewall and transmission tunnel) to attenuate engine noise and road noise entering the passenger compartment of the vehicle. Typical noise insulation mats require apertures since the surfaces of the vehicle include pass-through openings that accommodate various penetrating members, such as a steering column, electrical wiring, and ducting. These pass-through openings create problems with flanking noise that travels through the pass-through openings and into the passenger compartment thereby reducing the effectiveness of the noise insulation mat for any given thickness.
When fuel economy concerns were not as stringent as they are today and when higher horsepower engines were used, the noise insulation mats could be thicker, increasing both their weight and thereby their noise attenuation capability, without significant impact on vehicle performance. As vehicle fuel economy becomes an increasing priority, horsepower ratings must decrease and noise attenuation system weight allowances have decreased. This has forced noise attenuation system manufacturers to use lighter weight materials. Noise attenuation system weight has subsequently decreased, but at a tradeoff with the acoustic attenuation achieved. It has therefore become desirable to provide noise attenuation systems that provide attenuation levels similar to the prior thicker/heavier designs while providing the benefits of reduced weight.